Pigments are used in a wide variety of coatings such as, for example, paints, plastics, paper, laminates, corrosion resistant primers, decorative topcoats in the automotive, industrial or appliance markets. Coatings contain a mixture of solid and liquid materials that form a film when applied to a surface and the coating is allowed to cure. The solid material of a coating is a blend of pigments, fillers and resins. Typically, the pigment provides the hiding power and influences gloss and the resin forms the film when the coating is cured.
There have been significant efforts to produce pigments with desired characteristics (e.g., stability, viscosity, hiding power, tinting strength and/or gloss) for the particular application. Many prior art references describe surface treating the pigment with compounds such as for example, alumina, silica, phosphate, and/or silanes to impart the desired characteristic to the pigment for the particular end use application.
Other prior art references describe using one or more dispersing agents that may be added to a pigment or pigment slurry to obtain a coating having the above desired characteristics. These dispersing agents may be made, for example, by reacting an amine, such as for example, triethanolamine with a polyprotic acid, such as for example polycarboxylic acid. Typically, the mole ratio of amine to polyprotic acid is less than 3:1 (e.g., 1:1, 2:1, 2.5:1).
Unfortunately, some slurries made using prior art dispersing agents have reduced stability during storage because the pigment may separate out of the slurry rendering the slurry difficult to pump and transport. Upon incorporating the pigment into a suitable coating, the resultant hiding power, tinting strength and/or gloss of the coating may not be commercially acceptable.
There is a need for new pigment compositions and methods for producing commercially acceptable pigments at high throughput rates. Pigment compositions having improved stability, hiding power, tinting strength and/or gloss are also needed.